Fix /room/.../event/... to return the *original* event after any edits

changelog.d/12476.bugfix

@@ -0,0 +1 @@
+Fix a long-standing bug which incorrectly caused `GET /_matrix/client/r3/rooms/{roomId}/event/{eventId}` to return edited events rather than the original.

synapse/events/utils.py

@@ -402,17 +402,18 @@ def serialize_event(
         *,
         config: SerializeEventConfig = _DEFAULT_SERIALIZE_EVENT_CONFIG,
         bundle_aggregations: Optional[Dict[str, "BundledAggregations"]] = None,
+        apply_edits: bool = True,
     ) -> JsonDict:
         """Serializes a single event.
 
         Args:
             event: The event being serialized.
             time_now: The current time in milliseconds
             config: Event serialization config
-            bundle_aggregations: Whether to include the bundled aggregations for this
-                event. Only applies to non-state events. (State events never include
-                bundled aggregations.)
-
+            bundle_aggregations: A map from event_id to the aggregations to be bundled
+               into the event.
+            apply_edits: Whether the content of the event should be modified to reflect
+               any replacement in `bundle_aggregations[<event_id>].replace`.
         Returns:
             The serialized event
         """
@@ -430,8 +431,9 @@ def serialize_event(
                     event,
                     time_now,
                     config,
-                    bundle_aggregations[event.event_id],
+                    event_aggregations,
                     serialized_event,
+                    apply_edits=apply_edits,
                 )
 
         return serialized_event
@@ -470,6 +472,7 @@ def _inject_bundled_aggregations(
         config: SerializeEventConfig,
         aggregations: "BundledAggregations",
         serialized_event: JsonDict,
+        apply_edits: bool,
     ) -> None:
         """Potentially injects bundled aggregations into the unsigned portion of the serialized event.
 
@@ -479,7 +482,8 @@ def _inject_bundled_aggregations(
             aggregations: The bundled aggregation to serialize.
             serialized_event: The serialized event which may be modified.
             config: Event serialization config
-
+            apply_edits: Whether the content of the event should be modified to reflect
+               any replacement in `aggregations.replace`.
         """
         serialized_aggregations = {}
 
@@ -490,9 +494,10 @@ def _inject_bundled_aggregations(
             serialized_aggregations[RelationTypes.REFERENCE] = aggregations.references
 
         if aggregations.replace:
-            # If there is an edit, apply it to the event.
+            # If there is an edit, optionally apply it to the event.
             edit = aggregations.replace
-            self._apply_edit(event, serialized_event, edit)
+            if apply_edits:
+                self._apply_edit(event, serialized_event, edit)
 
             # Include information about it in the relations dict.
             serialized_aggregations[RelationTypes.REPLACE] = {

synapse/rest/client/room.py

@@ -669,8 +669,10 @@ async def on_GET(
             )
 
             time_now = self.clock.time_msec()
+            # per MSC2676, /rooms/{roomId}/event/{eventId}, should return the
+            # *original* event, rather than the edited version
             event_dict = self._event_serializer.serialize_event(
-                event, time_now, bundle_aggregations=aggregations
+                event, time_now, bundle_aggregations=aggregations, apply_edits=False
             )
             return 200, event_dict